X-ray lithography is a proximity patterning technique. A gold pattern X-ray mask is used to selectively absorb and transmit soft X-rays for exposing a resist-coated wafer held in close proximity to the mask. The X-ray mask itself comprises a thin substrate of BN, SiC or Ti that is supported by a rigid mounting ring. The gold mask absorber pattern is formed by etching a 7000 angstrum thick, gold film deposited on the substrate or by a special, low stress, gold plating process.
Soft 7 angstrum X-rays are generated by a high-power source, a water-cooled rotating anode and an electron gun located together in a vacuum chamber. X-rays are generated by focusing the hollow, cone-shaped beam of electrons onto the rotating tungsten surface of the anode. The cylindrical, high-powered electron gun allows the X-rays generated in a small diameter spot to pass through it. This diverging cone of X-ray radiation then passes through a thin beryllium vacuum window into a helium filled exposure chamber. The mask and wafer are closely aligned prior to insertion into the exposure chamber, and maintained during exposure.
The present invention is particularly directed to a new and improved X-ray mask ring assembly and apparatus for making same, which is significantly less complicated, less costly, and achieves a superior product with respect to such assemblies and apparatus employed heretofore.
Related patents in this field include, inter alia; U.S. Pat. Nos. 3,743,842 issued July 3, 1973; 3,892,973 issued July 1, 1975; 4,037,111 issued July 19, 1977; 4,085,329 issued Apr. 18, 1978; 4,185,202 issued Jan. 22, 1980; 4,187,431 issued Feb. 5, 1980; 4,215,192 issued July 29, 1980; 4,238,682 issued Dec. 9, 1980; 4,301,237 issued Nov. 17, 1981 and 4,335,313 issued Jan. 15, 1982.